The electrical detection of bio-molecules is currently an active research field. Two types of detection approaches are typically used. The first type is based on translocation of bio-molecules through nanometer-size ion channels across biological membranes or solid-state pores across dielectric membranes. The detection mechanism is based on the blockage of the electrical conductance of the pores during translocation events. This approach is capable of single bio-molecule analysis. However, due to the small sizes of the bio-molecules (DNAs in the referred studies), the size of the pores is required to be small (<˜10 nm) for appreciable current blockage signals, which imposes enormous fabrication challenges. The second type uses field effect to detect the biological charge of bio-molecules that are specifically immobilized to the sensor surface; this includes both planar ISFET structure and, more recently, nanowire structures. This affinity-type approach often detects the ensemble average signal of the immobilized bio-molecules. Electrolyte screening is known to impose a fundamental limit on its charge sensing capabilities at physiological condition. As an example, the characteristic Debye screening length in a physiological condition (˜100 mM salt concentration) is ˜1 nm.
In other research efforts, scientists have described DNA sequencing devices that use semiconductor field effect transistors at the surface of an opening or recess for charge detection of analytes flowing by in the close vicinity under electrophoresis process. Just as the ISFET type sensing scheme, such proposed devices are still limited by the electrolyte screening since no mechanisms are identified or designed to overcome that limit. Their charge sensing operation is dependent on the close proximity (˜Debye length) of bio-molecules to the sensing elements. Such devices propose relatively small-size openings (e.g., <˜10 nm), which enormously complicates the device fabrication steps. These devices also use metal and insulator layers to replace the p-doped or n-doped semiconductor regions. The operation of this type of device is based on the principle that the field effect will change the tunneling current across the insulator layer from one metal layer to another.
Accordingly, there is need for apparatuses and methods, involving the detection of bio-molecule charges, that overcome these and other limitations.